On the Inheritance of Muscular Dystrophy

Summary The results are reported of a survey of the mode of inheritance of muscular dystrophy, as determined from a series of 102 cases, of which 84 were examined personally. It is believed that this series approaches complete ascertainment of all cases at present recognized in the two counties of Northumberland and Durham. Available sibs and parents of affected individuals were examined whenever possible. It is agreed that rare ocular and distal forms of muscular dystrophy may be distinguished, but evidence is presented for suggesting that the commonly occurring cases can be classified into three types which are separate entities, both clinically and genetically. These maybe referred to as the Duchenne, facioscapulohumeral and limb‐girdle forms. A study of the mode of inheritance of the Duchenne type, in thirty‐four families containing fifty‐six cases, has indicated that the gene responsible for this disease is transmitted as a sexlinked recessive character with a high mutation rate. An estimation of the mutation rate in the present series gave a result of 4.3 × 10 ‐5 . It is believed that the occasional occurrence of this form of the disease in females is not entirely incompatible with the suggested mode of inheritance; furthermore, the classification of such cases within this group is essential in view of their clinical similarity to the affected boys. In four families of the facioscapulohumeral type, containing twenty‐two cases, an autosomal dominant mode of inheritance was clearly indicated, although there was a possibility of sex limitation in one family and of incomplete manifestation in another. Eighteen families of the limb‐girdle form were examined and yielded twenty‐one cases. Except for one family, in which an autosomal dominant gene may have transmitted the disease, the pattern of inheritance was compatible with an autosomal recessive mechanism. The information available concerning one case of ocular myopathy and two of distal myopathy was insufficient to establish the mode of inheritance. Detailed blood grouping of blood samples was carried out in affected individuals, and in their sibs and parents, in nine families of the Duchenne type, and three of the facioscapulohumeral. No linkage between the gene for any type of myopathy and that for any blood group was discovered. Colour vision was tested in all families of the Duchenne type. Red‐green colour blindness was discovered in one family only (D6), but the information was insufficient to decide whether the gene responsible for this defect was closely linked to that responsible for the muscular dystrophy.